package web.servlet;

import util.DownLoadUtils;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;

@WebServlet("/downLoadServlet")
public class DownLoadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1.获取请求参数,文件名称
        String filename = request.getParameter("filename");
        // 2使用字节输入流加载文件进内存
        // 2.1找到文件的服务器路径
        ServletContext servletContext = this.getServletContext();//获取servletContext对象(代表整个对象范围)
        // 2.2获取文件真实路径
        String realPath = servletContext.getRealPath("/img/" + filename);
        // 2.3用字节流关联
        FileInputStream fis = new FileInputStream(realPath);

        // 3设置response的响应头
        // 3.1设置响应头类型:content-type
        String mimeType = servletContext.getMimeType(filename);//获取文件的mine类型
        response.setHeader("content-type", mimeType);

        // 解决中文文件名问题
        // 1.获取user-agent请求头
        String agent = request.getHeader("user-agent");
        // 2.使用工具类方法编码文件名即可
        filename = DownLoadUtils.getFileName(agent, filename);

        // 3.2设置响应头打开方式:content-disposition
        response.setHeader("content-disposition", "attachment;filename=" + filename);

        // 4.将输入流的数据写到输出流中
        ServletOutputStream sos = response.getOutputStream();
        int len;
        byte[] bys = new byte[1024 * 8];
        while ((len = fis.read(bys)) != -1) {
            sos.write(bys, 0, len);
        }
        fis.close();
        sos.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
